List of by-elections to the Senedd
|Assembly term||By-election||Date||Incumbent||Party||Winner||Party||Cause||Retained at next election|
|2016–2021||Alyn and Deeside||6 February 2018||Carl Sargeant||Labour||Jack Sargeant||Labour||Death (suicide)||Yes|
|2011–2016||Ynys Môn||1 August 2013||Ieuan Wyn Jones||Plaid Cymru||Rhun ap Iorwerth||Plaid Cymru||Resignation to lead the Menai Science Park||Yes|
|2003–2007||Blaenau Gwent||29 June 2006||Peter Law*||Labour||Trish Law||Independent||Death (brain tumour)||Yes|
|1999–2003||Swansea East||27 September 2001||Val Feld||Labour||Valerie Lloyd||Labour||Death (cancer)||Yes|
*Peter Law left the Labour Party and sat as an independent prior to his death. The by-election was won by his widow, but is classed as an independent gain from Labour.